1. Field
The disclosure relates to a method, system, and article of manufacture for the control of information units in fibre channel communications.
2. Background
Fibre Channel refers to an integrated set of architectural standards for data transfer being developed by the American National Standards Institute. Fibre Connection (FICON) is a protocol of the fibre channel architecture and may also be referred to by the formal name of FC-SB3. Further details of FC-SB3 may be found in the publication, “FIBRE CHANNEL Single-Byte Command Code Sets-3 Mapping Protocol (FC-SB-3)”, Rev. 1.6, published by the American National Standards for Information Technology on Mar. 26, 2003.
A channel is a direct or a switched point-to-point connection between communicating devices. In the Fibre Channel architecture, a FICON channel may perform the functions specified by FC-SB3 to provide access to Input/Output (I/O) devices by means of control units or emulated control units. FICON channels may rely on packet switching for transferring data between communicating devices.
A channel command word (CCW) is a control block which includes an I/O request, and may refer to a structure of a specific system architecture which specifies a command to be executed along with parameters. A channel program is a sequence of one or more channel command words executed sequentially that controls a specific sequence of channel operations. FICON channels may transmit up to sixteen channel command words at a time along with the associated data for any write operations, where a channel command word may be referred to as an “information unit”. If more than sixteen information units are present in a channel program then after the transmission of the first sixteen information units the remaining information units may be transmitted in groups of eight until the channel program is completed.
Extended Remote Copy (XRC) is a copy function available for the z/OS* and OS/390* operating systems. XRC maintains a copy of the data asynchronously at a remote location, and can be implemented over extended distances, such as distances of over one hundred kilometers. XRC may be used in IBM Enterprise Storage Servers* (ESS). Further details of XRC may be found in the publication “IBM TotalStorage Enterprise Storage Server: Implementing ESS Copy Services with IBM eServer zSeries,” published by International Business Machines Corporation, in July, 2004. *z/OS, OS/390, and Enterprise Storage server are trademarks or registered trademarks of International Business Machines Corporation.